This invention relates generally to photocopiers and particularly to scanner drive assemblies for photocopiers.
Ordinarily the image that is copied in a photocopier is obtained from the original by scanning it. That is, a scanning assembly is effectively moved past the original, or the original, on a copyboard, is moved past a fixed lens arrangement. The image is relayed from successive portions of the original to the photosensitive drum of the photocopier and a copy is eventually made by transferring a developed image from the drum to a sheet of transfer material.
The relative movement of the original and the lens arrangement must be smooth and, preferably, rapid, for accurate, quick copying, the desired end of the typical photocopying system. The twin goals of smoothness and rapidity are to some extent inconsistent, since the rapid motion of the generally reciprocating scanning system will lead to abrupt starts and stops that jar the system.
Also, if there is any slippage of the relative position of elements in the system, the careful registration or correspondence of one element of the system to another may be lost. The abrupt starts and stops of the typical scanning system, made up of cables, chain drives and motor shafts, can lead to loss of reliable registration unless the system is carefully designed.
One typical scanner drive system employs a chain drive to turn a scanner cable pulley to move a scanning element (lens or mirror system or copyboard) back and forth. In one direction, the pulley is driven off the main photocopier drive shaft. On the return, the pulley is driven by a reverse motor, the connecting elements in the drive being sprocket wheels and a drive chain loop. In practice, it has been found that some "jitter" and loss of registration has occurred as a result of movement of the chain loop at the end of the return step.
Accordingly, it is an object of this invention to provide an improved scanner drive assembly that minimizes jitter and loss of registration. It is a further object to provide an inexpensive and reliable scanner drive system with minimum modification of existing systems.